Elf99 - rebirth of a classic

From: Ethan Dicks <erd_at_infinet.com>
Date: Mon Nov 9 17:13:15 1998

I originally wrote:
> < I have been in discussion with some folks about 1802's and the possibili
> < of producing a modern PCB for the Popular Electronics Elf design...
>
> < How authentic should a modern Elf be? Try to use 1822/2101 RAM or use

Allison Parent resonds:
> If you're building an elf then 2101, if your doing superElf go for 32k
> 62256.

If I can lay my hands on a quantity of 1822/2101 RAMs, then I agree,
even though they will cost as much as the CPU. The 6264 was a fallback.
In any case, I would decode 7 or 8 upper address bits if I went with
a larger SRAM and allow the user to stick in there what they wanted.
One other suggestion is room for a ROM. I could wire in two or three JEDEC
sockets and let the builder pick what to go in the, one 62256 or a couple
of 6264's and a 27128, for example.

The problem with replicating the SuperElf is the keyboard. I have no
idea where to get that chip from (74941?), nor an inexpensive source
for that many pushbuttons (including some latching ones). I can see
the keys coming to $2 to $3 each if bought from a standard vendor.
 
> < UART? Add an I/O port? Add nothing to the Quest PCB layout? Remove
> < nothing? ...
>
> The quest layout was the bare minimum elf. No expandability. I have one
> and expanding it is not appealing.

Agreed. I never expanded my Quest Elf. My mentor did, a mature fellow of 16
to my 11 at the time. He shoved in a machined pin wire wrap socket and
took it from there. He built his own 8-bit input port and 8-bit relay
driver output port by breadboarding the standard 44-pin Radio Shack prototype
boards. It worked, but it was non-trivial. I inserted the WW socket, but
never wrapped anything to it.

> An expandable elf would be of interest
> to me as I still have one (20 year old) 1802 doing not much.

Me, too. There are a couple ways of implementing expansion, Elf-II compatible
and COSMAC VIP compatible. The VIP used those ubiquitous 44-pin cards.
I would rather build in a compromise of universally desired features than
get into the position of making peripheral cards. In practice, I like
addon cards, but when it comes down to a very small production run, I'd like
to keep this to one board. Cards are nice when you have lots of users with
very different needs. With an Elf, beyond an I/O port and serial or video,
what's really necessary? What's so important that it raises the cost a few
bucks for everyone?
 
> < How much would anyone pay for such a thing? ...neighborhood of $40-$50,
> < depending on how many extras and the order size
>
> For the quest board that is expensive for the bare board.

I was thinking of extras like an area for the 1861 video, or a 2"x4"
perfboard prototyping area. In any case the Quest design wouldn't
be that expensive in sufficient quantities, but at q. 25, there's
a lot of setup charges to amortize over the small run of the boards. At
least $10 each (~$250 setup / 25 boards). If anyone can direct me
to a board house that will do a 6"x9" board with ~600 holes, three or
four sizes, plated through, with minimal setup charges, I'm all ears.
Unless I get *lots* of interest, I'm only considering a run of 25,
then that's it. I don't want to have 60 or 70 unsold boards hanging
around forever.

> < Yes, anyone who wants can still breadboard an 1802 together. It's a
> < pain...
>
> The base ELF was pretty trivial to build as the parts count was nothing.

40 pin CPU, 2x22 pin RAM, 11 switches, 2x7 pin displays, approx 10 CMOS
DIP parts x 14 or 16 pins, a handful of diodes and resistors... let's
say about 350 point-to-point connections, probably more. I breadboarded,
but never more than about 200 connections, and that was a DEC FLIP-CHIP
module tester for the VIC-20 (dual 6821 PIAs and a single DEC 36-pin
backplane connector).

The Quest kit was the base ELF plus a ROM socket and space for primary
and secondary power supplies. One suggestion for the Elf replica was
to use a standard 4-pin Molex connector and power it from a discarded
PC power supply. The Quest Elf kit just had two solder pads for 6.3V AC
or +5V DC. I ran mine from my VIP regulated +5v supply.

-ethan
Received on Mon Nov 09 1998 - 17:13:15 GMT